The present invention relates to an apparatus for instructing an operator to displace a gearshift to its optimum shift position so that the gears in a manual transmission are located in an optimum position, and more particularly to an apparatus for instructing an operator to displace a gearshift to its optimum upshift position so that the gears in a manual transmission are located in an optimum position in accordance with various running conditions of the vehicle.
It has been proposed that to achieve minimum fuel consumption in a vehicle equipped with a manual transmission, an operator should determine when to shift the transmission in accordance with observed values from a speedometer or a tachometer. A proposed apparatus instructs an operator to upshift to an optimum gearshift position to achieve the goal of minimum fuel consumption. According to this proposed apparatus, an upshift zone is predetermined by the parameters of engine speed (RPM) and an engine load. The apparatus is designed to detect the engine speed and the engine load, and subsequently instruct an operator to shift the manual transmission to its optimum location by using an indicator means when the parameters of engine speed and engine load fall within the upshift zone. This upshift zone comprises an area where the actual engine speed is greater than a predetermined engine speed and the actual engine load is less than a predetermined engine load. An apparatus which uses the aforementioned upshift zone instructs the operator to upshift when the vehicle is started or when the vehicle is accelerating. Further, when the vehicle is decelerating or idling, the apparatus is designed to instruct an operator that an upshift would be improper. Additionally, when a throttle valve opens only slightly, the apparatus is designed to instruct an operator that an upshift is necessary.
However, the aforementioned apparatus has the following disadvantages. When a vehicle maintains a certain vehicle speed, such as when coasting on a gentle downhill grade, an engine brake may take effect to slow the vehicle, resulting in the throttle valve slightly opening. Hence, the apparatus detects the slight opening of the throttle valve and instructs the operator that the transmission should be upshifted even though the engine is acting as a brake for the vehicle.
Further, according to the aforementioned apparatus, an improper upshift instruction issues at other specific running conditions, such as when the load on the engine is large (created by, for example, the vehicle climbing an incline) or when the vehicle is accelerating. Additionally, when a stroke of an accelerator pedal temporarily decreases to lower the speed of the vehicle, the engine speed slowly decreases, but results in a rapid decrease of the engine load. This causes the apparatus to issue an upshift signal because the engine operating parameters are within the upshift zone. However, if an uphill incline was to continue, the upshift instruction would be improper.